Idle speed control systems for internal combustion engines change throttle position to increase or decrease engine speed to a desired speed. Because the throttle is coupled to the air intake valve of multiple cylinders through an intake manifold, there is a delay time before the change in throttle position results in a change in engine torque and accordingly idle speed. Advancing or retarding ignition timing is therefore also used to provide a faster response time. However, advancing ignition timing beyond a steady state or nominal value may cause ignition knock. To prevent knock during idle speed control, the steady state value is retarded to an offset value so that ignition timing may be advanced when needed from the offset value to increase engine speed without inducing ignition knock.
The inventors herein have recognized that this retarded offset value reduces fuel economy and have sought to minimize the usage of such offsets. They also have recognized that idle speed control and regenerative braking can be combined in a way as described herein to enhance braking through an alternator driven by the engine while providing idle speed control with reduced usage of the retarded offset ignition timing and fast response time.
In one example, some of the above issues may be addressed by a method comprising: when decelerating a vehicle driven by an engine, recharging a battery by an alternator driven by said engine; and during engine idle speed control, when engine speed is less than desired, in a first mode reducing electrical power to selected devices, and in a second mode offsetting a set point of desired engine ignition timing to a new set point when engine speed is higher than desired. In this manner, fuel economy is improved by not creating a new retarded set point in a first mode of operation, fast response time is provided by disabling or reducing selected loads, and more regenerative braking is enhanced by battery recharging during deceleration and less during idle speed control. Thus, the alternator load may be reduced for quick-acting engine torque increase so long as some load exists in the alternator prior to the requisite engine torque increase.
The selected devices may comprise those electrical devices which if disabled or supplied with reduced electrical power would not be perceptible by an operator, such devices include one or more of the following: coolant fans, pumps, and heaters.
In another aspect, alternator torque is increased during vehicle deceleration to provide an additional braking force to the vehicle. Further, idle speed control commences when the vehicle slows to a preselected speed.
In another example, the method comprises: controlling idle speed of an engine coupled to an alternator which supplies electrical power to various electrical devices in a vehicle driven by said engine; a first mode of the engine idle speed control which is active when reducing or shutting off electrical power applied to selected ones of the electrical devices would be perceived by an operator of the vehicle; during the first engine idle speed control mode, offsetting a steady state ignition timing value of the engine in a retarded direction to an offset retarded value, and when the engine speed is less than desired advancing the ignition timing from the offset retarded value, and when the engine speed is greater than desired, retarding the ignition timing from the offset retarded value; a second mode of the engine idle speed control which is active when reducing or shutting off electrical power applied to said selected electrical devices would not be perceived by an operator of the vehicle; and during the second idle speed control mode, removing the offset retarded value, and disabling or reducing electrical power to the selected devices when the engine speed is less than desired, and retarding the ignition timing from the steady state ignition timing value when engine speed is higher than desired.
In a further example voltage regulation of electrical power provided by the alternator may be provided, the voltage regulation causing a reduction in torque of the alternator in response to the shutting off electrical power applied to the selected electrical devices.
In a further aspect, the nominal ignition timing corresponds to a steady state ignition timing and the offset ignition timing is set to allow the ignition timing advance without inducing ignition knock in the engine.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.